The instant invention relates to curing agents, methods for making the curing agents and their usage for curing epoxy resins.
Epoxy resins are typically brittle and have a low resistant to crack propagation. Extensive research has been generated to develop toughening agents of epoxy resins for high performance structural applications. However, the typical approach to improve the fracture toughness is the addition/pre-reaction of a dispersed phase in the epoxy resin; which implies an extra step in the preparation of thermosets, requiring additional mixing/heating capabilities increasing time and cost of production. The addition of a dispersed phase in the epoxy resin also modifies the viscosity of the resin, which is a critical parameter during the processing of structural applications. Therefore, there is a need in this art for a curing agent which offers the added value to improve fracture toughness without any additional processing step or increased viscosity. There is also a need in this art for an improved curing agent that possesses improved processability while avoiding usage of high viscosity toughening agents, for example, carboxy terminated polybutadine acrylonitrile (CTBN).
Examples of conventional curing agents and epoxy systems are disclosed in U.S. Pat. Nos. 5,003,004; 5,053,465; 5,278,257; 6,998,011; 7,037,217; 7,157,527; 7,705,102; 7,910,656; 7,951,879; and US Pub Nos 2011/0067813; 2011/0014257; 2011/0294963; and 2013/0037213. The disclosure of the foregoing patents and patent applications is hereby incorporated by reference.